Method for coating a plurality of liquid layers on a web



F b. 17, 1970 MAMdRUANb jsHlwA'rA E J 3, 96,

METHQD FOR COATING A PLURALI'I'Y OF LIQUID LAYERS ON A WEB File d Nov. 16, 1966 2 Shets-Sheet' 1 v 'INVENTORS MAMORUAND ISHIWATA TETUO YOSHIDA ATTORNEYS Feb. 17, 1970 MAMORLIAND' s -nw ETAL 3,496,005

v I METHOD FOR COATING A PLURALII 'Y or LQIIYQUID Lhawms ON A vim Fiied Nov. 16, 1966 v 2 Sheets-Shet 2 ATTORNEYS INVENTORS VMAMORUAND \smwATA TETUO YOSHIDA AW, @MMW/ WWW United States Patent 3,496,005 METHOD FOR COATING A PLURALITY 0F LIQUID LAYERS ON A WEB Mamoruand Ishiwata and Tetuo Yoshida, Ashigara- Kamigun, Kauagawa, Japan, assignors to Fuji Shashin Film Kabushiki Kaisha, Ashigara-Kamigun, Kanagawa, Japan Filed Nov. 16, 1966, Ser. No. 594,927 Claims priority, application Japan, Nov. 16, 1965, 40/ 69,970 Int. Cl. B44d 1/14, N08

US. Cl. 117-34 4 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method for applying one or more coating liquids in a layer or layers to the surface of a continuously travelling web.

In the conventionally employed bead coating or doctor coating methods, a support or a web is generally moved in such a way that the back side of the web to be coated is closely contacted with a rigid surface, such as a roller, for maintaining a constant clearance between the coating apparatus and the surface of the web. In such a conventional coating method however, there are the following difficulties:

(1) The clearance between the coating apparatus and the web is locally narrowed when foreign matter, deposited on or imbedded in the back surface of the web or the surface of the backing roller, passes through the coating section. This results in spot-like coating unevenness on the coated layer.

(2) For maintaining a constant clearance between the coating apparatus and the support, high precision is required in the coating device, backing roller and the thickness of the support. If the precision is lowered, the thickness of the coated layer will become uneven, particularly in the case of employing a doctor coating method.

(3) A specific means is necessary for enlarging the clearance between the coating apparatus and the support by moving the coating apparatus or the backing roller when the joint of the support passes through the narrow clearance and the operation of said means inevitably causes the formation of an improper coating over a considerable length of the joint portion of the support.

(4) For advancing the support, the backing roller is usually driven by an electric motor, and, in such case, the vibrations caused by the rotations of the motor and the backing roller are transferred to the support and the coating device, which results in the formation of lateral stripelike unevenness in the coated layer.

The above-mentioned difficulties obstruct accurate coating at a high production rate, and in particular, they become a large problem in a case where high quality and high yield are required in coating, such as, photographic light-sensitive elements.

3,496,005 Patented Feb. 17, 1970 The inventors have found that these difiiculties in coating can be overcome by conducting the coating in such a way that a continuously travelling support or web is floated by the pressure of a gas existing at the back side of the web to be coated when it passes through the coating section.

The invention will be fully understood by the following detailed explanations referring to the accompanying drawings, in which:

FIG. 1 is a schematic view showing the entire system for conducting an embodiment of the present invention;

FIG. 2 and FIG. 3 are enlarged cross-sectional views showing two embodiments of forming a single layer in accordance with the present invention, and

FIG. 4 and FIG. 5 are enlarged cross-sectional views showing two embodiments of forming multiple layers in accordance withthe present invention.

Referring now to FIG. 1 and FIG. 2, a web 1 to be coated, such as, a plastic film or a paper, is continuously moved at a constant speed in the direction indicated by the arrows by means of a conveyer 2 and is usually provided with a constant tension by a tension controlling means. A gas chamber 4, into which a pressurized gas, such as air, is supplied by means of a blower and the like is placed facing the back surface of the travelling web. The surface of the gas chamber 4 facing the web is provided with many small holes or slits 5. The gas jetted through the holes or slits forms a space 6' between said gas chamber 4 and the web 1, having a higher pressure than the side of the web surface to be coated. This floats the web out from the outer surface of the gas chamber with the distance defined by the tension of the web previously provided by tension means 3 and the gas pressure in the space, whereby the continuously travelling web follows a stable and definite path.

Free rollers 7 and 7 rotating with the same speed and in the same direction as those of the travelling web and a resistance plate 8 positioned on the transverse sides of the space formed between the gas chamber 4 and the free roller 7 are so placed that the abrupt outflow of the gas along the back surface of the web at the inlet and outlet portions of the web to the gas chamber section is prevented so that there is no flapping of the web.

At the side of the surface of the web which is to be coated there is placed a coating device composed of a doctor edge 9 and a coating liquid reservoir 12. Said doctor edge is placed at the position where the edge is slightly apart from or almost in contact with the surface of the web 1 travelling continuously while floating a slight distance from the outer surface of the gas chamber 4, or the doctor edge pushes the web slightly to the side of the gas chamber while maintaining a suitable distance from the surface of the gas chamber. The reservoir is so constructed that a coating liquid is always supplied to the space between the back side of the doctor edge and the surface of the web to be coated.

The coating liquid is withdrawn by the travelling Web through the clearance between the doctor edge and the web in a layer of a definite thickness determined by the travelling speed of the web, the strength of contact of the doctor edge with the surface of the web, the pressure of the coating liquid behind the doctor edge, the viscosity of the coating liquid and the like. Thus, the thickness of the coated layer may be controlled over a wide range by suitably selecting the above-mentioned conditions, and further, the thickness thereof may be maintained stably by keeping the conditions constant.

In another embodiment of this invention, shown in FIG. 3, a so-called slide-type bead coating means, having an inclined wall 15 and a coating liquid reservoir 12, is employed to apply a single layer of a coating liquid to a continuously travelling web 1 floating a slight distance from a gas chamber 4, similar to that of the type shown in FIG. 2.

The present invention is applicable in the case of forming multiple layers simultaneously, as shown in FIG. 4 and FIG. 5. That is, in one embodiment shown in FIG. 4, a three-layer coating means consisting of a combination of a doctor coating means, having a doctor edge 9 and a coating liquid reservoir 12, and a slide coating means, having inclined walls 16 and 17 and coating liquid reservoirs 13 and 14, is employed in the floating system of this invention. In the floating system, as shown in PEG. 4, however, the resistance plate 8 in FIGS. 1 to'3 is omitted and a gas chamber 4 of a specific structure and three free rolls are employed instead. Further, in still another embodiment of this invention, as shown in FIG. 5, a so-called multiple doctor type coating means having doctor edges 9, 10, and 11 and coating liquid reservoirs 12, 13 and 14 is employed.

The invention has been described referring to several specific embodiments but it wiil be understood that many other coating systems can be used in the invention.

In the case of conducting coating based on the principle of the present invention, the following merits or advantages can be expected, although there may be some differences depending upon the kind of coating device to be employed.

(1) Since the web is moved in a floating state by gas pressure, foreign matter deposited on or imbedded in the back surface of the travelling web does not push the web to the coating means side when the foreign matter passes through the coating section, and hence, such spot-like unevenness as is seen in the usual doctor coating method or bead coating method is not formed in the thus coated layer or layers.

(2) Since the web is moved in a floating state by gas pressure, it is unnecessary to move the coating device or a backing roller, as is the usual case in doctor or bead coating, when a joint of the web passes through the coating section. Hence, the length of the unsuitable coating on the web at the joint portion is extremely shortened, which improves the yield for the product.

(3) Since the gas chamber for floating the web is not rotated and the chamber is not contacted with the travelling support, it is unnecessary to place near the coating device a driving source for rotating a backing roller as in conventional doctor or bead coating methods. Hence, almost no coating unevenness is caused by transferring mechanical vibrations of the driving source to the web and coating device.

(4) Since the web is always pressed to a doctor edge at a definite pressure, the contact strength of the Web with the doctor edge is not substantially changed, even if the doctor edge has some defects in its accuracy or the Web has some irregularities in thickness. Hence, the formation of unevenness in the thickness of the coated layer, caused by poor accuracy, as observed in conventional doctor coating, is substantially prevented. This makes possible the coating of extremely thin layers together with the above-mentioned prevention of the formation of spot-like, coating unevenness, as compared with the case of using a conventional doctor coating method.

Since the web is pressed to the bead edge of the coating device at a constant pressure, the coating bead is neither flickered nor broken by the air stream carried by the travelling web. Hence, the coating can be conducted at a high speed and with reduced coating unevenness, as compared with a conventional bead coating method.

The invention will further be described with reference to the following examples:

Exampie 1 The coating for silver-halide type copying papers was conducted by the process of this invention using a coating apparatus as shown in FIG. 2 under the following con ditions:

Coating liquid: gelatino silver halide emulsion for copying papers; viscosity 20 cp.; density 1.05 g./cm.

Feeding rate of coating liquid: 2.5 liter/min./m. width.

Travelling speed of web: 50 m./ min.

Static pressure in gas chamber 4: 400 mm. H O gauge.

Distance of floating we: from the surface of gas chamber: 0.5 mm.

Clearance between the doctor edge 9 and the outer surface of gas chamber 4: 0.3 mm.

After coating, the layer was set immediately and dried. The thus coated layer had uniform distribution in thickness and no unevenness, showing that the copying paper had satisfactory qualities.

Example 2 The three-layer coating of gelatino silver halide emulsion for a positive cinecolor film was conducted on an under-coated cellulose triacetate film according to the present invention using the apparatus as shown in FIG. 4 under the following conditions:

Coating liquid for the first layer: blue-sensitive emulsion; viscosity 50 cp.; density 1.05 g./cm. feeding rate thereof 1.0 liter/min./m. width.

Coating liquid for the second layer: red-sensitive emulsion; viscosity 50* cp.; density 1.03 g./cm. feeding rate thereof 1.8 liter/min./m. width. I

Coating liquid for the third layer: green-sensitive emulsion; viscosity 50 cp.; density 1.04 g./cm. feeding rate thereof 1.2 liter/min./m. width.

Travelling speed of web: 30 m./min.

Static pressure in gas chamber 4: 500 mm. H O gauge.

Distance of the floated web from the surface of gas chamber 4: 0.5mm.

Clearance between the doctor edge 9 and the gas chamber 4: 0.15 mm.

After coating, the layers were set immediately and dried. The thus coated layers had uniform distribution in thickness, no unevenness, and no intermixing therein, which showed that the product had satisfactory qualities.

What is claimed is:

1. A method for evenly coating a plurality of liquid layers on the surface of a continuously moving web comprising:

(a) continuously moving said web around a fixed gas chamber, the portion of said chamber in proximity to said web having a perforated cylindrical surface,

(b) maintaining said -web a suitable distance from said gas chamber by floating saidweb by supplying pres surized gas through said perforations to the back surface of said "web whereby said web floated substantially-throughout thewhole surface of said chamber during its passagearound said cylindrical surface,

(0) simultaneously applying multiple superposed liquid coating layers to the surface of th'econtinuously moving webwhich is not impinged by saidv gas while maintaining-said web in a floated state, and

(d) continuously moving said coated web the remaining distance of the gas chamber while maintaining it in a floated state.

2. The method of claim 1 wherein while floating on said pressurized gas the surface of said web to be coated is contacted with the upper surface of a bath comprising a coating liquid, and passed over a doctor edge, the thickness of the resulting layer being determined by passage over said doctor edge.

3. The method as claimed in claim 1 wherein at least one of said coating liquids is a gelatino silver halide photographic emulsion.

4. The method as claimed in claim 1 wherein said coating is conducted by the combination of a doctor coating method and a bead coating method.

References Cited UNITED STATES PATENTS 1,831,064 11/1931 Frederick 11716 X 2,094,348 9/1937 Carlson 1171 11 3,019,130 1/1962 Horndostel 117-111 6 3,038,685 2/1963 Colgan 118410 3,113,884 12/1963 Kohler 118-410 WILLIAM D. MARTIN, Primary Examiner 5 WM. R. TRENOR, Assistant Examiner US. Cl. X.R. 

